Fiber optic technology is increasingly used in place of conventional electrical circuits and components for a variety of different functions. Advantages can include simplicity, reliability and, with decreasing cost of fiber optic components, decreased expense.
There are many instances when it is necessary or desirable to detect the presence or absence or the position of an object at a given location. One example is a printer used for reproducing material such as text or graphic output from a computer or other source. Typically a printer includes a mechanism for feeding paper in sheet or continuous form to a location where characters or other matter is printed onto the paper. In connection with the control of the printer or computer or the like, it is desired to determine whether or not paper is present at a location in the printer or associated paper feed mechanism. For this purpose, a sensor is used along the paper feed path to determine whether or not paper is present.
In the past it has been conventional to mount an electrical switch near the paper feed path. The typical switch used for this purpose includes a lever or arm in the paper path that is moved by paper in the path to operate the switch. Electrical conductors extend from the switch to remote circuitry, and the switch includes moving mechanical parts causing expense, complexity and the eventual need for replacement. Of course there are many other instances in which electrical switches and similar electrical circuit components have been used to detect the presence or position of an object at a given location, and all such instances are potentially subject to similar problems and disadvantages.
In order to overcome disadvantages incident to the use of electrical sensing devices, it would be desirable to use fiber optic techniques in place of electrical components. However, other problems arise in adapting fiber optic technology to an optical sensing system. The difficulties include connecting the ends of fiber optic capables with a simple and inexpensive assembly while achieving optimum use of transmitted light. Since the goal is to provide a reliable indication of the presence of an object, such as paper along a printer paper feed path, an accurate optical system must be provided to assure that the maximum amount of light is properly transmitted to and from a target area. This should be accomplished without complex and expensive optical components, without the necessity for critical manufacturing tolerances and without painstaking assembly or fabrication procedures.